1. Field of the Invention
The present invention relates to a dielectric heating device for thawing frozen goods by dielectric heating.
2. Description of the Prior Art
A Japanese utility model application Ser. No. 14125/75 (Utility Model Laid-open No. 95064/76) discloses a refrigerator provided with a thawing chamber, in which such frozen goods as frozen food are disposed between a pair of electrodes of a capacitor applied with a high-frequency voltage. The above capacitor and a coil make up a series resonance circuit which is used as the load of a power amplifier, and therefore the frozen goods serving as the dielectric of the capacitor can obtain a sufficient supply of high-frequency power. However, the electric impedance (namely, capacitance and inductance) of the capacitor, which contains between the electrodes thereof the frozen goods, varies with such factors as the shape and kind of the frozen goods and the thawing temperature, and therefore the resonance frequency of the resonance circuit is also varied. In order to effectively supply the frozen goods with high-frequency power, the oscillation frequency of a high-frequency power supply has to be made equal to the resonance frequency of the resonance circuit. In order to satisfy this requirement, there has been proposed a circuit, in which a variable capacitor is connected in parallel with the above capacitor, a variation in the resonance frequency of the resonance circuit including the variable capacitor is detected, and the capacitance of the variable capacitor is automatically controlled so as to suppress the detected variation. However, since an automatic control system is indispensable, the above circuit is complicated in circuit construction and is expensive.